Singapore has asked Indonesia to share evidence of any involvement by Singapore-linked companies or Singaporeans in illegal land-clearing practices in reply to comments by Indonesian Coordinating Minister for People's Welfare Agung Laksono alleging their role in the ongoing haze over Sumatra.

"The government of Singapore takes a serious view of these allegations," a spokesman for Singapore's Ministry of Foreign Affairs (MFA) said on Saturday in response to media queries on Agung's remarks.

"If there is credible evidence that Singapore-linked companies or Singaporeans were involved, the government of Singapore intends to take further steps against these errant companies and individuals."

Ongoing forest and peatland fires in Riau have razed at least 6,000ha of land, including significant portions of two nature conservation areas, Indonesian disaster officials said on Saturday as 1,046 hot spots were detected across Sumatra, 963 of them in Riau alone.

The province has declared an emergency till March 12 and reactivated a disaster command post at Pekanbaru's airbase. But the severe haze and poor visibility saw helicopters unable to carry out water-bombing operations on Saturday , leaving residents to cope with hazardous air quality.

Indonesian authorities have also stepped up enforcement action, but have yet to name suspects.

Agung said last Thursday Indonesian police had launched 41 investigations since last year against companies and individuals that may be involved in open burning. "Many are from Malaysia and Singapore," he said, in a report posted on his ministry's website.

The MFA spokesman said: "We would like to reiterate our call to the government of Indonesia to share the evidence relating to any involvement by Singapore-linked companies or Singaporeans."

Agung and other officials had, during last June's severe haze that saw pollutant levels over Singapore reach record highs, also implied Singapore companies were behind the haze. But subsequent investigations did not see any Singapore-linked companies or Singaporeans named as suspects.

On Saturday, MFA said it hoped the ongoing fires in Riau and other parts of Sumatra would be "quickly dealt with to prevent a recurrence of transboundary haze". "We also urge the government of Indonesia to take the necessary legal and enforcement action against errant companies or individuals, regardless of their nationality," it added.

"As we have said previously, the primary responsibility for legal and enforcement action lies with Indonesia, where these companies and individuals were allegedly conducting such illegal activities."

On Saturda, National Disaster Management Agency spokesman Sutopo Purwo Nugroho said some 1,500 soldiers, police officers, firemen and disaster officials have been deployed to put out fires at hot spots. "But the vast areas on fire, difficult access and a shortage of water makes extinguishing them difficult," he added.

Dr Sutopo said parts of the Giam Siak Kecil-Bukit Batu biosphere reserve and the Tesso Nilo National Park had been deliberately set on fire by who had built temporary huts in these areas. The pollutants standard index in Duri Field, near Dumai, reached 500 on Saturday and in Bengkalis, 375.